Microwave synthesis and antifungal evaluations of some chalcones and their derived diaryl-cyclohexenones

Abstract

Microwave irradiation (MWI) of acetophenones and substituted benzaldehydes in water resulted in a “green-chemistry” procedure for the preparation of chalcones (1-14), through base catalyzed Claisen-Schmidt condensation reaction, in good yields. Further 3,5-diaryl-6-carbethoxy-2-cyclohexen-1-ones (1a-14a) were prepared through base catalyzed cyclocondensation of above chalcones with ethylacetoacetate using MWI as the energy source and silica as support. Out of fourteen cyclohexenones, ten (1a, 4a, 5a, 6a, 7a, 9a, 10a, 11a, 12a and 13a) are reported for the first time in literature. The synthesized compounds were characterized using various spectroscopic techniques, viz. (¹H NMR and IR) and screened for their antifungal activity in vitro against Sclerotium rolfsii and Rhizoctonia solani by poisoned food technique. The compounds tested were found to be active against R. solani whereas against S. rolfsii, moderate activity was observed, as evident from LC₅₀ values. The most potent compounds against R. solani were 1-(4-Fluoro-phenyl)-3-phenyl-propenone (13) and 1,3-Diphenyl-propenone (14) having LC₅₀ values of 2.36 and 2.49 mgL^{− 1} respectively (LC₅₀ of Hexaconazole = 1.12 mgL^{− 1}) and against S. rolfsii 3-(4-Fluoro-phenyl)-5-(3-nitro-phenyl)-6-carbethoxy-2-cyclohexen-1-one (12a) was most active having LC₅₀ value of 285 mgL^{− 1}compared to Hexaconazole (LC₅₀ = 1.27 mgL^{− 1}).

Keywords:

• Microwave irradiation (MWI)
• chalcones
• diaryl-cyclohexenones
• fungicidal activity
• cyclocondensation
• Sclerotium rolfsii
• Rhizoctonia solani

A part of this paper was presented at the National Symposium on Green Chemistry: Applications in Science & Engineering, February 5–6, 2009, Thapar University, Patiala, India.